WO2000033728A1

WO2000033728A1 - Method and apparatus for determining spectral sensitivity of receptors

Info

Publication number: WO2000033728A1
Application number: PCT/HU1999/000094
Authority: WO
Inventors: György ÁBRAHÁM; Gottfriedné Wenzel
Original assignee: Coloryte Hungary Optikai Kutató, Fejleszto És Gyártó Rt.
Priority date: 1998-12-04
Filing date: 1999-12-06
Publication date: 2000-06-15
Also published as: HUP9802809A3; HU9802809D0; AU1790500A; HUP9802809A2

Abstract

The invention relates to an apparatus for determining spectral sensitivity parameters of colour-sensitive receptors in the eye, comprising first optical means (1, 6, 7, 8, 9, 10, 11, 12) for generating a substantially monochromatic first testing light beam of variable wavelength, optical elements (13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24) for generating a second testing light beam, second optical means (1, 2, 3) for generating an auxiliary light beam consisting of white light reducing colour adaptation of the receptors to testing light beams, third optical means (4, 5) for introducing the first testing light beam onto a measuring area of the retina of the eye and for introducing the auxiliary light beam onto an area of the retina of at least the same size as the measuring area, and an optical element (4) in said third optical means for directing either the first testing light beam and the auxiliary light beam, or the second testing light beam and the auxiliary light beam onto the retina.

Description

METHOD AND APPARATUS FOR DETERMINING SPECTRAL SENSITIVITY OF RECEPTORS

TECHNICAL FIELD

The invention relates to a method and an apparatus for determining spectral sensitivity parameters of colour-sensitive receptors in the eye.

BACKGROUND ART

The human eye is able to detect electromagnetic radiation in the wavelength range of visible light, which extends from approx. 380 nm to 780 nm. There are three colour-sensitive receptors (pigments) assuring colour vision, called protos which is sensitive to red, deuteros which is sensitive to green, and tritos which is sensitive to violet. Sensation of the yellow colour is generated by simultaneous stimulation of the protos and the deuteros. Simultaneous stimulation of the tritos and the deuteros causes the vision of the colour turquoise, while simultaneous stimulation of the tritos and the protos leads to the sensation of the colour purple. Other transitional shades of colours are produced by simultaneous stimulation of the three receptors with different intensities.

Diagrams of spectral sensitivity of the protos, the deuteros and the tritos for people having normal (average) colour vision are known. It is known furthermore that the sensitivity of colour-sensitive receptors increases substantially if the intensity of illumination decreases and it drops significantly if the illumination intensity is higher. This kind of phenomenon is called adaptation, which takes place in each receptor independently of each other to a different extent, if the intensity of illumination does not change uniformly in the total spectrum range, but has a lower influence on certain receptors and higher influence on others. This is called chromatic adaptation (Leo M. Hurvich: Color Vision, Sinauer Associates Inc., Sunderland, Massachusetts, USA, 1981 , pp. 196-200).

It is also known that people do not have exactly the same colour vision. According to the current state of medical art, there are so-called colour blind people who only see two basic colours instead of three. If there is a lack of protos receptors, the colour blind person is called protanop, in lack of deuteros receptors, we speak about a deuteranop person, and if tritos receptors are missing, the person is called tritanop. Additionally, there are people with anomalous colour vision suffering in parachromatism. Although they have all the three receptors, they have a sensation of colours which deviates from that of a normal person. The most frequent form of anomalous colour vision appears as red-green parachromatism. People suffering in red-green parachromatism do not recognise pseudo-isochromatic tables (known in practice as dotted figures) and they are not able to distinguish between red, yellow and green signals used in traffic control. Different types of parachromatism are described on pages 222-269 of the textbook of Leo M. Hurvich mentioned above.

Since people suffering in parachromatism are handicapped in numerous fields of life compared to individuals of normal colour vision, various solutions have already been recommended for correcting the error of colour vision. In WO 95/05621 , the difference between an eye with a colour vision to be corrected and the eye with normal colour vision is compensated by a colour filter of a transmission characteristic selected on the basis of the abnormal spectral sensitivity of the protos, deuteros and tritos receptors of the eye with the colour vision to be corrected. In order to select the colour filter, the spectral sensitivity curves of the person suffering in parachromatism must be measured and the displacement of the curves along the wavelength must be determined.

It is known that the spectral sensitivities of receptors in the eye can be determined by individual measurements (W.B. Marks, W.H. Dobbelle, E.F. Mac Nichol: Visual Pigments of Single Primate Cones, Science, Vol.143, March 1964). Rushton performed microspectrographic measurements on eyes of living human beings and monkeys (W.A.H. Rushton: Visual Pigments and Color Blindness, Scientific American, March 1975). In this method, a thin monochromatic light beam is imaged on the retina through the pupil of the eye to be tested, with the size of the light beam - when reaching the retina - not exceeding that of a cone bearing a protos, deuteros or tritos receptor. The intensity of the light beam is continuously measured prior to entering and also after being reflected by the receptor. The difference of the two values corresponds to the intensity of light absorbed by the given receptor, which is characteristic of the receptor's sensitivity in the given wavelength. By changing the wavelength of the testing light beam, the spectral sensitivity curve of the given receptor can be determined. Since the sensitivity of one receptor on one cone is measured at a time, in this method it is not a problem that the spectral sensitivity ranges of the receptors are in overlap in most part of the visible spectrum. However, the measurement of the extremely low light intensity and the implementation of demanding measuring conditions do cause a problem.

A test similar to the one described above has been carried out by a spectrophotometric measurement on colour blind people or on samples removed from the person's retina (L.C. Thomson, W.D. Wright: The Convergence of the Tritanopic Confusion Loci and the Derivation of the Fundamental Response Functions, JOSA, 1953, Vol. 43, No. 10, pp. 890-894). These persons have one or more receptors missing, therefore the overlap of spectral sensitivity ranges does not disturb the measurement and so it is not necessary to locate the measurement to a single cone having one type of receptor. However, this method is only suitable for testing colour blind people and not for examining people suffering in parachromatism or having normal colour vision.

According to another method, the spectral sensitivity curves of receptors can be defined by a mathematical method from results of colour mixing measurements (Dr. Klara Wenzel and Dr. Gabor Szasz: Numerical method for determining simultaneous functions measured with an indirect measuring method (in Hungarian), Finommechanika-Mikrotechnika, 1985, Vol. 24, No. 8/9, pp. 250- 252). Results obtained by this computing method are in line with the results of the mentioned microspectrographic measurements, however, the measurements and the calculations are time-consuming.

These known methods are relatively complicated and require costly equipment as well as operating personnel of special qualifications.

In WO 95/28125, a method and apparatus are described for determining spectral sensitivity parameters of colour-sensitive receptors in the eye. The method is characterised in that one or two testing light beams are introduced onto an area of the retina in the eye to be tested and the sensitivity parameters are determined by detecting a light beam reflected from the retina or by using the visual perception of the tested person. In addition to said testing light beam(s), one or two auxiliary light beams of a wavelength falling outside the spectral sensitivity wavelength range of the colour-sensitive receptor or receptors to be measured are also introduced onto at least the same area of the retina, said auxiliary light beam(s) reducing the sensitivity of colour-sensitive receptor or receptors not to be measured. By means of this so-called blinding method, the wavelength corresponding to the maximum sensitivity of the receptors and the wavelength values where the sensitivity of the receptors drops below a certain threshold can be adequately measured.

However, the blinding method and the apparatus described in the application above have several disadvantages. According to the method, the intersection of the spectral sensitivity curves of two types of receptors can be found at the point where the colour corresponding to one receptor changes to the other. However, in practice, finding the boundary of the two colours is a difficult task, because the spectrum is continuous, and by changing the wavelength continuously different colours are seen. In addition, when measuring the point of intersection, the application of the blinding auxiliary light beam reduces the sensitivity of the third receptor not to be measured, but exactly as a result of selecting the wavelength of the blinding auxiliary light beam it practically fails to make any impact on the receptors to be measured. Therefore, when approaching the intersection slowly from one direction along the wavelength, the eye of the tested person is adapted to the perceived colour of the testing light beam, and this decreases the sensitivity of the colour-sensitive receptor. The decreasing of sensitivity entails a shifting of the intersection, which falsifies the measurement. Therefore, this known method is less suitable for determining the intersection of the spectral sensitivity curves of two receptors.

DISCLOSURE OF INVENTION

It is an object of the invention to provide a method by which the spectral sensitivity parameters of colour-sensitive receptors in the eye can be determined simply, but more exactly than earlier, even under routine testing conditions. It is another object of the invention to provide an apparatus which can be used in general ophthalmologic practice, also enabling a control of test results, for determining the spectral sensitivity parameters of colour-sensitive receptors.

On the one hand the invention is based on the idea that the spectral sensitivity curves can be determined with appropriate accuracy on the basis of wavelength values corresponding to particular points of the spectral sensitivity curves, so it suffices to identify these parameters of the sensitivity curves, only.

On the other hand, the invention is based on the further consideration that in determining the spectral sensitivity parameters of colour-sensitive receptors in the eye, the measurements are to be preferably carried out in the state of the receptors when they are adapted to the colour white, and at the same time the colour perception of the tested person can be utilised during the measurement - even in the case of people suffering in parachromatism. The state adapted to the colour white stabilises the sensitivity curves, and so the measuring results, even the wavelengths corresponding to the intersections of sensitivity curves, can be reproduced and compared to each other. On the basis of our experiments we have recognised that not only persons of correct vision but also people suffering in parachromatism have colour notions suitable for determining the sensitivity curve parameters of the tested eye.

According to a first aspect, the invention is a method for determining spectral sensitivity parameters of colour-sensitive receptors in the eye, in the course of which a testing light beam is introduced onto a first area of a tested person's retina comprising protos, deuteros and tritos receptors, an auxiliary light beam is introduced onto a second area of the retina, the second area being of at least the same size as the first area, and at least one parameter of sensitivity curves of the receptors is determined on the basis of visual perception of the tested person. According to the invention, the auxiliary light beam consists of white light reducing colour adaptation of the receptors to the testing light beam, and the at least one parameter is determined on the basis of the colour perception of the tested person, said colour perception resulting from the stimulation of the receptors by the testing light beam.

By using an auxiliary light beam consisting of white light, that is a light having a generally uniform spectral energy distribution in the perception range of the human eye, the colour adaptation of the receptors in the retina is reduced and they are kept in a state adapted to the white light. Thereby it is ensured that during the measurement of the spectral sensitivity parameters, the receptors remain in a steady state adapted to the colour white, and since there is no colour adaptation, the measurement results do not depend on the duration of the measurement and on the direction of changing the wavelength of the testing light beam.

According to a preferred embodiment, the at least one parameter is determined by setting a colour perception corresponding to an equal stimulation of the protos and deuteros receptors, or the protos and tritos receptors, or the deuteros and tritos receptors of the tested person.

This embodiment is based on the consideration that the monochromatic colours appearing at the intersections of the sensitivity curve pairs of the receptors can be reliably defined for most people and thus also for people suffering in parachromatism. These monochromatic colours can be characterised by the colour notions turquoise, green and yellow. This is surprising because it is a widely held belief that people suffering in parachromatism have wrong colour notions. It is our experience, however, that for example yellow colour perception prevails also at people suffering in parachromatism when their own anomalous protos and deuteros receptors are subjected to equal stimulation. The development of the yellow notion is not deteriorated by correcting information received from the environment concerning this colour. This is because from the yellows of different spectra, people suffering in parachromatism statistically obtain the common information that on the average the stimulation of their protos and deuteros receptors were equal.

In certain cases of parachromatism, the sensitivity curves of protos, deuteros and tritos receptors have an intersection at substantially the same wavelength. If the eye is subjected to a stimulation created by a monochromatic light of such a wavelength, all the three receptors will be under stimulation of substantially the same extent. This results in achromatic, i.e. white or grey colour perception.

Therefore, the measuring of the intersection points is carried out preferably by applying a substantially monochromatic testing light beam of a constant intensity and variable wavelength, and by continuously changing the wavelength of the testing light beam, wavelength values associated with the yellow, green and turquoise colours corresponding to respective intersections of the sensitivity curves of the protos and deuteros receptors, the protos and tritos receptors, and the deuteros and tritos receptors, or alternatively that associated with white or grey colour corresponding to a common intersection of the sensitivity curves of the protos, deuteros and tritos receptors are determined.

When in certain cases of parachromatism, the sensitivity curves of protos and deuteros receptors are juxtapositioned in a certain range, the point of intersection cannot be accurately identified. In such a case, through continuously changing the wavelength of the testing light beam upper and lower limits of a wavelength range corresponding to a yellow colour perception resulting from the approximate juxtaposition of the sensitivity curves of the protos and deuteros receptors can be determined, and then these two wavelength values are used for determining the curves.

In a further preferred embodiment of the method, the at least one parameter is an upper and a lower wavelength limit value at which the image of the testing light beam disappears for the tested person. These limit values are preferably determined by continuously changing the wavelength of a substantially monochromatic testing light beam of constant intensity and variable wavelength. In this way, the upper and lower limit values of the eye's sensitivity range under the given background intensity is obtained, which parameters are important in determining the sensitivity curves.

Another preferred embodiment of the invention is characterised in that the testing light beam comprises a first substantially monochromatic light beam and a second substantially monochromatic light beam, wherein the wavelength of the first substantially monochromatic light beam is adjusted in the sensitivity range of a first receptor, for example the protos, and the wavelength of the second substantially monochromatic light beam is adjusted in the sensitivity range of a second receptor, for example the deuteros, and by changing the intensities of the first and second substantially monochromatic light beams in relation to each other, the colour associated with the same state of excitement of the first and second receptors is found, for example the yellow colour, and from the intensity ratio so adjusted, the sensitivity ratio of the two receptors at the wavelengths of the first and second substantially monochromatic light beams is determined. This measurement may also be carried out concerning the colour turquoise, by the stimulation of the deuteros and tritos receptors.

By means of this so-called colour mixing measurement, the sensitivity curves calculated from the parameters obtained by the method can be controlled, because the ratios obtained from the colour mixing measurement are redundant data, by which - compared to the sensitivity curves - the correctness of the parameters identified can be reviewed.

The auxiliary light beam and the testing light beam are preferably introduced onto the retina continuously and simultaneously.

The testing light beam is preferably introduced onto a 1 to 5° measuring area of the retina, and the auxiliary light beam is preferably imaged onto a 10 to 20° area covering substantially concentrically the measuring area.

In another preferred embodiment of the method, the first area of the retina for the testing light beam is a measuring area, and the second area of the retina for the auxiliary light beam is an area being larger than the first area and surrounding the first area substantially concentrically.

According to another aspect, the invention is an apparatus for determining spectral sensitivity parameters of colour-sensitive receptors in the eye, comprising first optical means for generating a substantially monochromatic first testing light beam of variable wavelength for determining the parameters of sensitivity curves of the protos, deuteros and tritos receptors in the eye to be tested, second optical means for generating an auxiliary light beam for facilitating the determination of the parameters of the sensitivity curves, and third optical means for introducing the first testing light beam onto a measuring area of the retina of the eye and for introducing the auxiliary light beam onto an area of the retina of at least the same size as the measuring area. According to the invention, the apparatus comprises optical elements in said second optical means for generating an auxiliary light beam consisting of white light reducing colour adaptation of the receptors to testing light beams, optical elements for generating a second testing light beam and introducing it onto the measuring area of the retina, wherein the second testing light beam enables controlling the sensitivity curves calculated from the parameters determined by means of the first testing light beam, and an optical element in said third optical means for directing either the first testing light beam and the auxiliary light beam, or the second testing light beam and the auxiliary light beam onto the retina.

In a preferred embodiment of the apparatus said first optical means comprise optical elements for generating the first testing light beam so as to consist of a substantially monochromatic light of continuously variable wavelength and constant intensity. Preferably, said first optical means comprise a stepped grey wedge for setting the intensity of the first testing light beam, a continuous interference filter for changing the wavelength of the first testing light beam, and a unit connected to the continuous interference filter for enabling reading of the wavelength value set.

In a second preferred embodiment of the apparatus the optical elements for generating the second testing light beam comprise means for generating two substantially monochromatic light beams of variable wavelengths and intensities. This embodiment preferably comprises two filter switches for setting the wavelengths of the two substantially monochromatic light beams of the second testing light beam, stepless grey wedges for changing the intensities of the two substantially monochromatic light beams, and units connected to the grey wedges for enabling reading of the intensity value set. The two substantially monochromatic light beams of the second testing light beam are generated preferably from the light of a first light source.

In an other preferred embodiment of the apparatus said second optical means further comprise optical elements for generating a further auxiliary light beam consisting of a light reducing the sensitivities of two types of receptors of the retina. The auxiliary light beam consisting of white light reducing colour adaptation of the receptors or the further auxiliary light beam consisting of a light reducing the sensitivities of two types of the receptors of the retina are preferably generated from the light of a second light source according to the setting of a filter switch.

The first testing light beam and the auxiliary light beam are generated preferably from the light of the second light source.

A further advantageous embodiment of the apparatus comprises an optical element for setting the spectrum of the auxiliary light beam, an optical element for adjusting the wavelength of the first testing light beam, an optical element for setting the intensity of the first testing light beam, optical elements for setting the spectrum of the second testing light beam and optical elements for adjusting the spectral intensity of the second testing light beam, wherein these optical elements and the optical element directing either the first testing light beam and the auxiliary light beam, or the second testing light beam and the auxiliary light beam onto the retina are controlled via interfaces by a computer.

Based on the apparatus according to the invention, a measuring instrument can be built, which can be widely used in ophthalmologic practice for recording the spectral sensitivity parameters of colour-sensitive receptors of people suffering in parachromatism. These curves are necessary for making glasses or contact- lenses for correcting parachromatism.

BRIEF DESCRIPTION OF DRAWINGS

Hereinafter, the invention will be described by means of preferred embodiments as shown in the drawings, where

Fig. 1 is a diagram depicting the white light adapted spectral sensitivity curves of the colour-sensitive receptors in the normal human eye, where the wavelength values measurable by the method and apparatus according to the invention and the points corresponding to these wavelength values are indicated,

Fig. 2 is a diagram depicting the white light adapted spectral sensitivity curves of the colour-sensitive receptors in a human eye with anomalous colour vision used as an example, with the points as per Fig. 1 ,

Fig. 3 is a diagram depicting the white light adapted spectral sensitivity curves of an eye exhibiting colour vision anomaly, where the sensitivity curves intersect each other substantially at a common point,

Fig. 4 is a diagram depicting the white light adapted spectral sensitivity curves of an eye exhibiting colour vision anomaly, where a yellow sensing range prevails resulting from the juxtaposition of the spectral sensitivity curves of the protos and deuteros receptors in the eye,

Fig. 5 is a schematical optical drawing of a preferred embodiment of the apparatus according to the invention,

Fig. 6 is a simplified block diagram of the computer control of the apparatus according to Fig. 5, and Fig. 7 is a flowchart of the measurement carried out by the preferred embodiment according to Fig. 5.

MODES FOR CARRYING OUT THE INVENTION

Fig. 1 shows white light adapted spectral sensitivity curves P(λ), D(λ), T(λ) of the colour-sensitive receptors in the normal human eye, where the vertical axis depicts in % the relative spectral sensitivity S corresponding to the colour perception generated in the brain, and the horizontal axis shows the wavelength λ in nm. On the vertical axis, the sensitivity is compared to the maximum of the sensitivity curve D(λ).

The spectral sensitivity curves adapted to white light, i.e. to a light having essentially uniform spectral energy distribution in the sensitivity wavelength range of the eye, are characterised in that the sizes of areas below the three sensitivity curves are substantially equal.

It can be seen that the maximum of the protos sensitivity curve P(λ) is at approx. 580 nm, that of the deuteros sensitivity curve D(λ) is at approx. 545 nm and that of the tritos sensitivity curve T(λ) is at approx. 448 nm. The intersection of the sensitivity curves T(λ) and D(λ) is at approx. 503 nm, that of the sensitivity curves T(λ) and P(λ) is at approx. 524 nm, and that of the sensitivity curves D(λ) and P(λ) is at approx. 575 nm. Under the same background intensity, the upper sensitivity wavelength limit value where the protos receptors no longer sense the light is at approx. 670 nm. At the same background intensity, the lower sensitivity wavelength limit value where the tritos receptors no longer sense the light is at approx. 380 nm. The maximum loci, the loci of intersections, the wavelength limit values and to a certain extent the shapes of the sensitivity curves may differ in various ethnic groups.

Fig. 2 shows as an example the white light adapted sensitivity curves P^*(λ), D*(λ), T*(λ) of the corresponding receptors of a human eye exhibiting colour vision anomaly. Again in this figure, the sensitivity S on the vertical axis is compared to the maximum of the sensitivity curve of the deuteros receptor. The sensitivity curve P*(λ) is shifted in the direction of the shorter wavelengths and is wider than the sensitivity curve P(λ). Since the area sizes below the sensitivity curves are substantially equal, the height of the wider curve P^*(λ) is smaller than that of the sensitivity curve P(λ). The sensitivity curve D^*(λ) is also shifted in the direction of shorter wavelengths compared to the sensitivity curve D(λ) and its shape is slightly narrower than the shape of the sensitivity curve D(λ). The sensitivity curve T^*(λ) is practically not shifted along the wavelengths, but its shape is different from that of the sensitivity curve T(λ).

Figs. 1 and 2 depict those particular points of the sensitivity curves the associated wavelength values of which can be determined by the method and apparatus according to the invention. These are the wavelengths of the maxima of the curves, the lower and upper sensitivity wavelength limit values, between which the receptors detect light under the given background intensity, and the wavelengths associated with the intersections of sensitivity curves, where the sensitivities of the receptors are equal for each pair. By means of these wavelengths or a subset thereof, as described below, the spectral sensitivity curves can be calculated with appropriate accuracy.

In each case when the protos and deuteros receptors are subjected to equal stimulation which can happen under both wide band and narrow band stimulation, yellow colour perception is developed. In the case of monochromatic or substantially monochromatic light stimulation, the yellow colour perception appears at the wavelength of the intersection of the sensitivity curves of protos and deuteros receptors. In the case of normal colour vision, this intersection point is at around 575 nm as depicted in Fig. 1 , and in the case of an anomalous colour vision, it is at approx. 559 nm according to Fig. 2.

When deuteros and tritos receptors are subjected to equal stimulation, the perception of the colour turquoise is developed. According to Fig. 1 , in the case of normal colour vision this can be generated at a wavelength 503 nm approximately, and in the case of an anomalous colour vision as per Fig. 2 this can be generated at a wavelength 496 nm approximately with a monochromatic light. In the two figures, the intersections of the sensitivity curves of deuteros and tritos are at these wavelengths. When protos and tritos receptors are under equal stimulation, this leads to the perception of the colour purple. However, this perception can not be generated by means of a single monochromatic colour, because in the vicinity of the intersection of the sensitivity curves of these two receptors, the sensitivity of deuteros receptors is nearly at the maximum. Accordingly, the intersection of the sensitivity curves of protos and tritos receptors can be identified by finding the clearest green colour perception of the tested person, where the green colour perception is influenced minimally by the other two receptors. The clearest green colour perception is at around 524 nm in the case of normal colour perception on a monochromatic or substantially monochromatic scale, and it is at around 512 nm in the case of an anomalous colour vision as per Fig. 2.

In certain cases of parachromatism, the spectral sensitivity curves of protos, deuteros and tritos receptors have an intersection at almost the same wavelength of the spectrum. Such a case is depicted in Fig. 3. If the eye is under stimulation with a monochromatic light of a wavelength corresponding to the common intersection, then the stimulation of all the three receptors will be substantially equal. In this case, achromatic, i.e. white or grey colour perception is developed. This most frequently arises at around 495, 510 and 525 nm. In Fig. 3, the common intersection point is at approx. 496 nm. In the depicted case, the person suffering in parachromatism does not perceive the colour turquoise on the monochromatic scale, because the intersection of the sensitivity curves D^*(λ) and T^*(λ) of the deuteros and tritos receptors is made achromatic by the sensitivity curve P^*(λ) of the protos receptor. The wavelength of the common intersection is also an important data for determining the spectral sensitivity curves.

Fig. 4 shows such a parachromatism case, when due to a juxtaposition of the spectral sensitivity curves P^*(λ) and D^*(λ) of the protos and deuteros receptors, the tested person perceives the colour yellow in a certain range of the monochromatic scale. In such a case it is difficult to find the intersection of the curves P*(λ) and D*(λ), but the upper and lower limits of the yellow range corresponding to the juxtaposition of the curves can be found. The depicted yellow range shown as an example is between 580 nm and 670 nm. The upper and lower limits of the yellow range are also important data in determining the spectral sensitivity curves.

In the course of finding the wavelengths corresponding to the intersections, the wavelength limit values of the perception and the limits of the yellow range, the tested person sometimes remains in the same wavelength range for several seconds. In the course of this, the phenomenon of colour adaptation arises, meaning that the sensitivity of the colour-sensitive receptor most sensitive in the given range substantially decreases, i.e. the sensitivity curve of the receptor shrinks in the vertical direction. As a result, the location of the point corresponding to the wavelength changes, which leads to a measuring error. According to the invention, this is eliminated by projecting an auxiliary light beam simultaneously and continuously with the substantially monochromatic testing light beam, on an area of preferably 10 to 16° enclosing concentrically the preferably 2° measuring area illuminated by the testing light beam, wherein the auxiliary light beam consists of white light of uniform spectral energy distribution in the perception range of the human eye. The white background light is preferably added to the testing light beam. Thereby it is accomplished that during the measurement of the wavelengths, the spectral sensitivity curves are principally in a steady state adapted to the white light.

Alternatively, the auxiliary light beam can also be projected onto a much larger area surrounding the measuring area of the retina. In this case the richness and brightness of the perceived colour of the testing light beam are not reduced by the white light of the auxiliary light beam. In this case, the receptors in the measuring area are subjected to the white light reducing colour adaptation as a result of the unintentional or intentional "wandering" of the eye, and this ensures that the receptors are adapted to the white light.

The substantially monochromatic testing light beam as an example could have a spectrum of approx. 10 to 20 nm half-width.

Consequently, the wavelengths corresponding to the intersections of the sensitivity curves, the wavelength limit values of sensitivity and in the given case the limits of the yellow range are preferably measured by introducing onto the measuring area a substantially monochromatic testing light beam of continuously variable wavelength and constant intensity, and by introducing an auxiliary light beam consisting of a constant intensity white light onto an area much larger than and comprising concentrically the measuring area. By continuously changing the wavelength, the tested person is asked to find the turquoise, green and yellow colour perception or in the given case the achromatic colour perception, and the upper and lower limits of the yellow range, respectively. The wavelength values corresponding to these colour perceptions are noted.

Furthermore, by means of the substantially monochromatic testing light beam of continuously variable wavelength, the upper and lower wavelength limit values at which the image of the testing light beam disappears for the tested person are determined. The upper wavelength limit value is the upper sensitivity limit wavelength of the protos receptor under a given background intensity, and the lower wavelength limit value is the lower sensitivity limit wavelength of the tritos receptor under the given background intensity. These upper and lower wavelength limits represent two more data for determining the spectral sensitivity curves. In this measurement, the auxiliary light beam also prevent the continuous adaptation of the receptors to the disappearing testing light beam. Without this, the outcome of the measurement would heavily depend on the duration thereof. The upper and lower sensitivity wavelength limit values shown in Figs. 1 and 2 apply to the background light of an auxiliary light beam used as an example.

During these measurements, the intensity of the testing light beam and that of the auxiliary light beam is preferably adjusted in a way that the perception generated by them is of equal magnitude.

The method according to the invention can be completed with a procedure known per se to determine the maximum locations of the spectral sensitivity curves of receptors. Also in this procedure the substantially monochromatic testing light beam of constant intensity and variable wavelength is introduced onto the measuring area of the retina. The spectrum of the auxiliary light beam applied to an area which includes but is much larger than the measuring area is adjusted, however, in a way that it falls into the sensitivity range of the two types of receptors not intended to be involved in the measurement, but so that the receptor to be measured is at the most subjected to stimulation at its peripheral wavelength range. Thereby, through the adaptation of receptors it is accomplished that the sensitivity of the receptor to be measured is much higher than that of the receptors not intended to be measured. In the course of this so-called blinding measurement, in the sensitivity wavelength range of the receptor to be measured, the wavelength of the testing light beam is adjusted until it is perceived to be the most intensive by the tested person. This wavelength will be the maximum point of the measured receptor's sensitivity curve.

This procedure can be carried out by three adjustments of the auxiliary light beam's spectrum, when two receptors are always blinded, and the maximum location of the sensitivity curve of the receptor not blinded is determined by the substantially monochromatic testing light beam. For measuring the maxima of the curves, the intensity of the auxiliary and testing light beam compared to each other is preferably adjusted in a way that the perception generated by the auxiliary light beam is much higher than that generated by the testing light beam.

The inventive method also provides a control opportunity for controlling the sensitivity curves calculated from the points identified by the procedure above. By the so-called colour mixing procedure, according to the invention, again an auxiliary light beam consisting of white light is used, but the testing light beam comprises two summed substantially monochromatic light beams, where the wavelength of one substantially monochromatic light beam is adjusted to fall into the perception range of a first receptor, for example the protos, and the wavelength of the other substantially monochromatic light beam is adjusted to fall into the sensitivity range of another receptor, for example deuteros. In the course of the procedure, by changing the intensities of the two substantially monochromatic light beams in relation to each other, the colour - in this case yellow - associated with the equal state of excitement of the first and second receptors is found, and from the adjusted intensity ratio the sensitivity ratio of the two receptors at the wavelengths of the two substantially monochromatic light beams is determined. The adjustment of the colour yellow is preferably carried out by the tested person, who continuously changes in opposite directions the intensities of the two substantially monochromatic light beams.

The obtained sensitivity ratio represents a redundant value, by which the sensitivity curves calculated from the measuring points above can be checked. On the basis of the model it can be determined in advance which intensity ratio will be adjusted by the tested person at the given wavelengths during the colour mixing measurement. If the intensity ratio adjusted by the tested person deviates substantially from the calculated extent, for example when the deviation goes beyond a specified tolerance limit, the sensitivity parameters must be re- determined by repeated measurement. Control by redundant values is especially advantageous because identifying any of the points erroneously could largely falsify the model consisting of calculated sensitivity curves.

Consequently, by means of the above steps, the characteristic wavelength values of the spectral sensitivity curves of the receptors as per Figs. 1 to 4 can be determined. Through the application of well known mathematical methods, the measured wavelength values are used for calculating the sensitivity curves of the receptors. It can be an advantageous way of calculating the curves when curves sought in a predetermined shape are matched to the measured points. The spectral sensitivity curves can be preferably approached by Gauss curves, for the plotting of which two parameters are required, and so for the plotting of the three Gauss curves, six parameters are necessary. Accordingly, when using a Gauss- curve based approximation, six points must be determined. They are advantageously the intersection of protos and deuteros curves, the intersection of protos and tritos curves, the intersection of deuteros and tritos curves, the upper wavelength limit value of sensitivity, the lower wavelength limit value of sensitivity and the maximum location of the tritos curve.

The sensitivity curves may also be approximated with different curves, for example the Weibull or experimental curves. In such a case, for example the method of least squares can be applied as a matching method.

The apparatus according to the invention is described on the basis of a schematical optical drawing of a preferred embodiment as shown in Fig. 5.

The preferred embodiment depicted in Fig. 5 has two possible operating modes. In the first operating mode, the light of a light source 1 is introduced onto the retina of the tested eye by means of a collector lens 2, a filter switch 3, a 50 % divider cube 4 and an ocular 5. Depending on the actual measuring process, this auxiliary light beam serves for fixing the white adapted state or in the blinding measurement for reducing the sensitivity of the two types of receptors not intended to be measured. Accordingly, by switching over the filter switch 3, an auxiliary light beam consisting of white light reducing colour adaptation of the receptors or an auxiliary light beam consisting of a light reducing the sensitivity of two types of the receptors of the eye can be generated. The filter switch 3 is preferably equipped with a unit enabling reading of the adjusted filter parameters.

By means of flat mirrors 6 and 7 and a collector lens 8, the light of the light source 1 is furthermore introduced onto a continuous interference filter 9 or to another identical purpose component based on a different principle, from which a substantially monochromatic light beam of adjusted wavelength exits. This substantially monochromatic light beam is guided to the retina of the tested eye by means of a stepped grey wedge 10 or a light intensity regulator based on a different principle, a collector lens 11 , a flat mirror 12, the 50 % divider cube 4 and the ocular 5. This substantially monochromatic light beam is a first testing light beam, the wavelength of which is adjusted by the continuous interference filter 9 and its intensity by the stepped grey wedge 10. The continuous interference filter 9 and the stepped grey wedge 10 are fitted with respective units enabling reading of the adjusted values.

In this first mode of operation, the measurements relating to the intersections and maxima of the sensitivity curves as well as the measurements relating to the upper and lower sensitivity wavelength limit values and to the upper and lower limits of the yellow range can be carried out.

The stepped grey wedge 10 is required because according to the description above, in the blinding measurement relating to the maxima of the sensitivity curves, the stimulation generated by the auxiliary light beam must be much higher than the stimulation caused by the testing light beam. To make sure that during the measurements relating to the maxima it is not necessary to apply an auxiliary light beam of a very high intensity, the intensity of the testing light beam is reduced by the stepped grey wedge 10.

In a second operating mode of the apparatus according to the invention, the light of the light source 1 is again introduced onto the eye by means of the collector lens 2, the filter switch 3, the 50 % divider cube 4 and the ocular 5. In the second mode of operation, using filter switch 3, an auxiliary light beam is generated which consists of white light reducing colour adaptation of the receptors. In this mode of operation, the divider cube 4 is adjusted in a way that it directs the auxiliary light beam together with a second testing light beam to the retina. Fig. 5 shows the divider cube 4 in this position.

The second testing light beam is generated from the light of a light source 13. From one side, the light of the light source 13 is introduced by means of a collector lens 14, a stepless grey wedge 24 or a light intensity regulator based on a different principle and a filter switch 15 to a flat mirror 16 and from there by a collector lens 17 to a 50 % divider cube 18. From the other side the light of the light source 13 is also guided to the divider cube 18 by means of a flat mirror 19, a collector lens 20, a filter switch 21 , a stepless grey wedge 22 and a collector lens 23. The substantially monochromatic light beams generated by the filter switches 15 and 21 are summed by the divider cube 18, and the second testing light beam so generated is introduced onto divider cube 4, which guides the auxiliary light beam and the second testing light beam by means of the ocular 5 to the retina of the eye to be tested.

In this second mode of operation, the colour mixing measurement can be carried out. In the course of this process, the tested person must adjust the colour sought by the additive mixing of the two substantially monochromatic light beams making up the second testing light beam. The intensity adjustment is implemented by the tested person preferably by moving the stepless grey wedges 22 and 24 in opposite directions. The stepless grey wedges 22 and 24 as well as the filter switches 15 and 21 are equipped with respective units enabling reading of the adjusted values.

The apparatus according to the invention is preferably designed in a way that the first testing light beam or the second testing light beam is introduced onto a measuring area of the retina, while the auxiliary light beam is introduced to an area including the measuring area, and being significantly larger than the measuring area.

The inventive apparatus can also be controlled by a computer 30 in a way shown in Fig. 6, which depicts the optical elements controlled by the computer 30 and their interfaces as a block diagram. It can be seen that the filter switch 3 is linked through an interface 32, the continuous interference filter 9 through an interface 33, the stepped grey wedge 10 through an interface 34, the divider cube 4 through an interface 35, the filter switch 15 through an interface 36, the filter switch 21 through an interface 37, the stepless grey wedge 22 through an interface 38 and the stepless grey wedge 24 through an interface 39 to a central interface 31 , which central interface 31 is connected to the computer 30. In such a way, the adjustment of these optical components and the reading of adjusted values can be carried out by means of the computer, which makes measurement and evaluation more reliable and faster.

A flow diagram of a measurement as an example by the apparatus according to Fig. 5 and controlled by the computer 30 is shown in Fig. 7. During the measurement, the stepped grey wedge 10, the filter switches 3, 15 and 21 as well as the divider cube 4 are actuated under the control of the computer 30. At the start of the measurement, the particulars of the tested person are entered. In the next phase, the tested person adjusts the colours yellow, green and turquoise, or in the given case the white or grey colour or lower and upper limits of the yellow range, by the manual movement of the continuous interference filter 9, as well as the upper and lower sensitivity wavelength limit values, where this wavelength values are registered by the computer 30 by means of a position detector connected to the continuous interference filter 9. In the meantime, the filter switch 3 is in a position which generates the white auxiliary light beam.

For measuring the maximum location of the tritos sensitivity curve, by changing over the filter switch 3 using computer 30, an auxiliary light beam blinding the protos and deuteros receptors is adjusted, and the intensity of the testing light beam is reduced by a computerised actuation of the stepped grey wedge 10. By moving the continuous interference filter 9, the tested person now finds the most intensive violet colour, the wavelength of which is registered by the computer 30 through the position detector.

In the next step, by changing over the divider cube 4, the apparatus is changed to the second mode of operation. For the colour mixing measurement, the filter switch 3 is returned to the previous position so that the auxiliary light beam is of the colour white again. By means of filter switches 15 and 21 , a substantially monochromatic red light beam is adjusted, which falls into the sensitivity range of the protos and a substantially monochromatic green light beam, which falls into the sensitivity range of the deuteros. The tested person adjusts the colour yellow by the displacement of the stepless grey wedges 22 and 24 in opposite directions. By means of the position detector associated with the stepless grey wedges 22 and 24, the computer 30 registers the mixing ratio.

In the next step, on the basis of the measured wavelength values, a model is set up for the sensitivity curves by for example Gauss-curve based matching, and it is calculated which intensity ratio can be expected by colour mixing, on the basis of the model. In case the adjusted intensity ratio deviates from the model set up by an extent higher than 2.5 times of the scatter characterising the apparatus - as an example -, the measurement is repeated. If the adjusted intensity ratio is within this tolerance limit, the diagram of the three sensitivity curves of the tested person is shown on the screen of the computer 30.

By means of the method and apparatus according to the invention, the sensitivity curves of colour-sensitive receptors can be determined much more accurately than earlier. This has a high significance in correcting parachromatism based on the accurate measurement of colour vision, but they can also be used for performing more accurately the screening tests of colour vision.

It will be evident to those skilled in the art that the above disclosure is exemplary only and that various other alternatives, adaptations and modifications may be made within the scope of the present invention as defined by the following claims.

Claims

1. A method for determining spectral sensitivity parameters of colour- sensitive receptors in the eye, in the course of which a testing light beam is introduced onto a first area of a tested person's retina comprising protos, deuteros and tritos receptors, an auxiliary light beam is introduced onto a second area of the retina, the second area being of at least the same size as the first area, and at least one parameter of sensitivity curves of the receptors is determined on the basis of visual perception of the tested person, characterised in that the auxiliary light beam consists of white light reducing colour adaptation of the receptors to the testing light beam, and the at least one parameter is determined on the basis of the colour perception of the tested person, said colour perception resulting from the stimulation of the receptors by the testing light beam.

2. The method according to claim 1 , characterised in that the at least one parameter is determined by setting a colour perception corresponding to an equal stimulation of the protos and deuteros receptors, or the protos and tritos receptors, or the deuteros and tritos receptors of the tested person.

3. The method according to claim 2, characterised in that the testing light beam is a substantially monochromatic light beam of constant intensity and variable wavelength, and the at least one parameter is constituted by wavelength values associated with the yellow, green and turquoise colours corresponding to intersections of the sensitivity curves of the protos and deuteros receptors, the protos and tritos receptors, and the deuteros and tritos receptors, respectively, said wavelength values being determined by continuously changing the wavelength of the testing light beam.

4. The method according to claim 2, characterised in that the testing light beam is a substantially monochromatic light beam of constant intensity and variable wavelength, and the at least one parameter is constituted by a wavelength value associated with the white or grey colour corresponding to a common intersection of the sensitivity curves of the protos, deuteros and tritos receptors, said wavelength value being determined by continuously changing the wavelength of the testing light beam.

5. The method according to claim 2, characterised in that the testing light beam is a substantially monochromatic light beam of constant intensity and variable wavelength, and the at least one parameter is constituted by an upper limit and a lower limit of a wavelength range corresponding to a yellow colour perception resulting from a substantial juxtaposition of the sensitivity curves of the protos and deuteros receptors, said upper and lower limits being determined by continuously changing the wavelength of the testing light beam.

6. The method according to claim 1 , characterised in that the testing light beam is a substantially monochromatic light beam of constant intensity and variable wavelength, and the at least one parameter is constituted by an upper wavelength limit value and a lower wavelength limit value at which the image of the testing light beam disappears for the tested person, said upper and lower wavelength limit values being determined by continuously changing the wavelength of the testing light beam.

7. The method according to claim 1 , characterised in that the testing light beam comprises a first substantially monochromatic light beam and a second substantially monochromatic light beam, wherein the wavelength of the first substantially monochromatic light beam is adjusted in the sensitivity range of a first receptor, for example the protos, and the wavelength of the second substantially monochromatic light beam is adjusted in the sensitivity range of a second receptor, for example the deuteros, and by changing the intensities of the first and second substantially monochromatic light beams in relation to each other, the colour associated with the same state of excitement of the first and second receptors is found, for example the yellow colour, and from the intensity ratio so adjusted, the sensitivity ratio of the two receptors at the wavelengths of the first and second substantially monochromatic light beams is determined.

8. The method according to claim 1 , characterised in that the auxiliary light beam and the testing light beam are introduced onto the retina continuously and simultaneously.

9. The method according to any of claims 1 to 8, characterised in that the first area of the retina for the testing light beam is a measuring area, and the second area of the retina for the auxiliary light beam is an area being larger than the first area and covering the first area substantially concentrically.

10. The method according to claim 9, characterised in that the testing light beam is introduced onto a 1 to 5° area of the retina, and the auxiliary light beam is introduced onto a 10 to 20° area of the retina.

11. The method according to any of claims 1 to 8, characterised in that the first area of the retina for the testing light beam is a measuring area, and the second area of the retina for the auxiliary light beam is an area being larger than the first area and surrounding the first area substantially concentrically.

12. An apparatus for determining spectral sensitivity parameters of colour- sensitive receptors in the eye, comprising first optical means for generating a substantially monochromatic first testing light beam of variable wavelength for determining the parameters of sensitivity curves of the protos, deuteros and tritos receptors in the eye to be tested, second optical means for generating an auxiliary light beam for facilitating the determination of the parameters of the sensitivity curves, and third optical means for introducing the first testing light beam onto a measuring area of the retina of the eye and for introducing the auxiliary light beam onto an area of the retina of at least the same size as the measuring area, characterised by comprising optical elements (1 , 2, 3) in said second optical means for generating an auxiliary light beam consisting of white light reducing colour adaptation of the receptors to testing light beams, optical elements (4, 5, 13, 14, 15, 16, 17, 18, 19, 20, 21 , 22, 23, 24) for generating a second testing light beam and introducing it onto the measuring area of the retina, wherein the second testing light beam enables controlling the sensitivity curves calculated from the parameters determined by means of the first testing light beam, and an optical element (4) in said third optical means for directing either the first testing light beam and the auxiliary light beam, or the second testing light beam and the auxiliary light beam onto the retina.

13. The apparatus according to claim 12, characterised in that said first optical means comprise optical elements (1 , 6, 7, 8, 9, 10, 11 , 12) for generating the first testing light beam so as to consist of a substantially monochromatic light of continuously variable wavelength and constant intensity.

14. The apparatus according to claim 13, characterised in that said first optical means comprise a stepped grey wedge (10) for setting the intensity of the first testing light beam, a continuous interference filter (9) for changing the wavelength of the first testing light beam, and a unit connected to the continuous interference filter (9) for enabling reading of the wavelength value set.

15. The apparatus according to claim 12, characterised in that the optical elements (13, 14, 15, 16, 17, 19, 20, 21 , 22, 23, 24) for generating the second testing light beam comprise means for generating two substantially monochromatic light beams of variable wavelengths and intensities.

16. The apparatus according to claim 15, characterised in that the optical elements (13, 14, 15, 16, 17, 19, 20, 21 , 22, 23, 24) for generating the second testing light beam comprise two filter switches (15, 21) for setting the wavelengths of the two substantially monochromatic light beams of the second testing light beam, stepless grey wedges (22, 24) for changing the intensities of the two substantially monochromatic light beams, and units connected to the grey wedges (22, 24) for enabling reading of the intensity value set.

17. The apparatus according to claim 16, characterised in that the optical elements (13, 14, 15, 16, 17, 19, 20, 21 , 22, 23, 24) for generating the second testing light beam comprise a first light source (13) from the light of which the two substantially monochromatic light beams of the second testing light beam are generated.

18. The apparatus according to claim 12, characterised in that said second optical means further comprise optical elements (1 , 2, 3) for generating a further auxiliary light beam consisting of a light reducing the sensitivities of two types of receptors of the retina.

19. The apparatus according to claim 18, characterised in that the optical elements (1 , 2, 3) of the second optical means comprise a filter switch (3) and a second light source (1) from the light of which the auxiliary light beam consisting of white light reducing colour adaptation of the receptors or the further auxiliary light beam consisting of a light reducing the sensitivities of two types of the receptors of the retina are generated according to the setting of the filter switch (3).

20. The apparatus according to claim 19, characterised in that the first testing light beam and the auxiliary light beam are generated from the light of the second light source (1).

21. The apparatus according to claim 12, characterised in that it comprises an optical element (3) for setting the spectrum of the auxiliary light beam, an optical element (9) for adjusting the wavelength of the first testing light beam, an optical element (10) for setting the intensity of the first testing light beam, optical elements (15, 21) for setting the spectrum of the second testing light beam and optical elements (22, 24) for adjusting the spectral intensity of the second testing light beam, wherein these optical elements and the optical element (4) directing either the first testing light beam and the auxiliary light beam, or the second testing light beam and the auxiliary light beam onto the retina are controlled via interfaces (31 , 32, 33, 34, 35, 36, 37, 38, 39) by a computer (30).